Electronic tube shield



Jul 16, 1957 D. J, DE CAIN ELECTRONIC TUBE SHIELD Filed Oct. 31. 1952 IN V EN TOR. DON/9L0 4/. 05 C/Q/N HTTOR/VEY.

United States Patent '0 ELECTRONIC TUBE SHIELD Donald J. De Cain, MountVernon, N. Y., assignor to General Precision Laboratory Incorporated, acorporation of New York Application October 31, 1952, Serial No. 317,888

9 Claims. (Cl. 313-312) This invention relates to shields for electronictubes and especially to tube shields facilitating heat dissipation.

Electronic tubes require electrostaticshielding'in many applications.Frequently tubes also have to be shock mounted, and when the tubeenvelope is fastened to a base by means of a spring clip theconventional type of tube socket shock mounting cannot be used. .Aproblem is presented when clip fastening, shock mounting andelectrostatic shielding are all required and the problem is complicatedby the necessity for dissipating the heat generated inside the tube.

The problem is particularly acute with subminiature tubes when they aremounted by clipping the envelopes to a base card, as they frequentlyare. It is desirable to make the tube shield integral with andinseparable from the tube, to facilitate stocking and replacement, yetto incorporate in the shield the function of protecting the tube frommechanical shock.

The present invention solves this problem by covering the glass tubeenvelope with a form fitting metal sheet separated from the envelope bya layer of heat-conductive rubber-like material. This material issecurely and permanently bonded both to the glass envelope and to themetal shield. The metal shield thus constitutes a solid external surfacewhich can be gripped positively by the metal spring clip whichmechanically secures the tube to the base card.

The principal purpose of this invention then is to provide a shield forelectronic tubes which not only shields the tube electrostatically, butalso protects the tube against mechanical shock while facilitating heatdissipation.

A further purpose of this invention is to provide a shield forsubminiature tubes, the shield being integrally associated with the tubeso as to facilitate stocking, mounting and replacement.

A complete understanding of this invention may be secured from thedetailed description and drawings, in which:

Figure 1 is a plan view of a subminiature tube partly enclosed in acover in accordance with the invention.

Figure 2 is an enlarged cross section of the tube and cover of Fig. 1along the line 22. I

Referring now to Fig. 1, a subminiature tube 11 is provided with a cover12 that is both shock absorbent and heat dissipative as well asconstituting an electrostatic shield. The cover 12 is securely bondedand attached to the tube envelope, and is clipped by means of metalclips 13 and 13' to a card 14 of insulating material. Connections may bemade between the tube terminal wires such as 16 and other componentseither directly or through terminals such as 17 by means of connectingwires or so-called printed conductive strips on the front or rear faceof the card 14.

In the cross section of Fig. 2 the glass tube envelope is indicated at18. Surrounding the envelope 18 there is a two-layer cover. The firstlayer 19 is made of a,

ice

rubber-like material which is firmly and continuously bonded to theglass envelope at all points. This material consists of a siliconerubber loaded or impregnated with a quantity of metal particles toincrease its heat conductivity. Any metal particles may be employed suchas copper, aluminum, silver or zinc, and the particles may be of anyconvenient small size. The silicone rubber is resilient and thethickness of the layer is sufficient to provide mechanical shockprotection for the tube. For example, in the case of a subminiaturecylindrical tube envelope having a diameter of inch, a thickness ofsilicone rubber of A inch has been found to be satisfactory.

The silicone rubber layer is surrounded by a metallic shield 21, the twobeing firmly and permanently bonded together. The shield 21 serves as amechanical protection for the silicone rubber layer and as a base forthe mechanical support by clips of the entire tube and jacket assembly.In addition the shield 21 serves as an electrostatic tube shield and asan external heat radiating and conducting surface for dissipating thetube heat.

The tube and cover assembly is firmly gripped and held by the springclips 13 and 13, these clips being riveted at 22 and 22 to the base 14.A ground wire 23 is desirable because of the electrostatic shieldingfunction of the shield 21. As a specific example of one tube coverassembly, a subminiature tube type 5902 having an outer envelopediameter of 0.375 inch is provided with a shield made to a similar shapebut inch larger at all points and therefore having an inner diameter of0.5 inch. The shield is made of & inch copper sheet formed into a roundbottomed cup by punching and die forming. The silicone rubber layer iscompounded starting with uncured silicone rubber having the consistencyof soft putty. Into this is thoroughly mixed 5% to 50% of electrolyticcopper dust. A primer coating of silicone resin varnish is applied tothe interior of the copper cup, the mixture placed into the copper cup,and then the subminiature tube is pressed into the cup and positionedcentrally thereof. The waste extruded compound is removed and theassembly is baked at C. for one hour to cure the silicone rubber. Noprimer coating is necessary for the glass tube envelope. In curing, thesilicone rubber expands slightly to fill all voids, sets and becomesresilient, and bonds firmly to both the glass tube envelope and theinterior of the copper cup. After trimming any excess silicone rubberfrom the edge of the cup the assembly is ready for clipping to the card14 and for making terminal connec tions.

This method of securing and shielding the tube thus provides good heatdissipation while protecting the tube from injury by mechanical shockand permitting the use of conventional clip mounting. The siliconerubber with stands the highest temperatures to which it can here besubjected. The assembly takes but little space, and stocking andreplacement of the covered tube as a unit are no more diflicult thanstocking and replacing the bare tube.

What is claimed is:

1. An electronic tube cover assembly comprising, an electronic tubehaving an envelope, a layer of resilient, heat-conductive siliconematerial bonded to the outer surface of said envelope, and an exteriormetallic layer bonded to the outer surface of said resilientheat-conductive material.

2. A shield for an electronic tube comprising, a thickness ofrubber-like material containing silicone bonded to the outside envelopeof said electronic tube, and metallic electrostatic shielding meansbonded to the outer surface of said rubber-like material thickness.

3. A shield for an electronic tube having a glass enhaving relativelyhigh heat conductivity bonded to the outer surface of said envelope, anda metallic shell securely bonded to the outer surface of said layer ofsilicone rubber.

5. A shock-resistant, heat-transmitting shield for the envelope of anelectronic tube comprising, a sheath of resilient silicone rubbercontaining an admixture of finely divided metallic particles and havingrelatively high heat conductivity, said sheath being bonded to the outersur face of the envelope of said electronic tube, and a metallic cupbonded to the outer surface of said sheath to form a surrounding shell.

6. A shock-resistant, heat-transmitting shield for the envelope of anelectronic tube in accordance with claim 5 in which said finely dividedmetallic particles consist of electrolytic copper dust.

7. A shock-resistant, heat-transmitting shield for the envelope of anelectronic tube in accordance with claim 6 in which the electrolyticcopper dust in said admixture is of from 5% to 50% of the quantity ofsaid silicone rubber.

8. An electronic tube cover and clip assembly comprising, an electronictube having an envelope, a layer of resilient heat-conductive siliconematerial bonded to the outer surface of said envelope, an exteriormetallic layer bonded to the outer surface of said resilientheat-conductive material, and spring clip means partly surrounding saidmetallic layer for securing it to a base.

9. An electronic tube cover and clip assembly comprising, a layer ofresilient silicone rubber containing metallic particles and havingrelatively high heat conductivity bonded to the outer surface of saidelectronic tube, a metallic shell securely bonded to the outer surfaceof said layer of silicone rubber, and spring clip means partlysurrounding said metallic layer for securing it to a base.

References Cited in the file of this patent I UNITED STATES PATENTS

9. AN ELCTRONIC TUBE COVER AND CLIP ASSEMBLY COMPRISING, A LAYER OFRESILIENT SILICONE RUBBER CONTAINING METALLIC PARTICLES AND HAVINGRELATIVELY HIGH HEAT CONDUCTIVITY BONDED TO THE OUTER SURFACE OF SAIDELECTRONIC TUBE, A METALIC SHELL SECURELY BONDED TO THE OUTER SURFACE OFSAID LAYER OF SILICONE RUBBER, AND SPRING CLIP MEANS PARTLY SURROUNDINGSAID METALLIC LAYER FOR SECURING IT TO A BASE